Oil burners are employed in various types of apparatus, such as boilers, furnaces, water heaters, etc. In such applications, an oil burner receives a fuel oil and initiates combustion thereof to generate heat which is then employed in various manners to perform work. Although several types of oil burners exist, one exemplary oil burner is illustrated in prior art FIG. 1, and is designated at reference numeral 10. The oil burner 10 comprises a blower housing 12 having an air tube 14 extending therefrom. The air tube 14 contains a combustion head affixed or positioned at one end 16 of the air tube opposite the housing 12, the end 16 having a nozzle and electrode assembly (not shown) positioned thereat. The nozzle is coupled to a fuel pump 18 by a fuel or nozzle line (a portion of which is highlighted at 20) for delivery of fuel oil thereto. The electrode assembly in the air tube 14 is coupled to a transformer or other type ignition device 22 residing on a top portion 24 of the housing 12.
As seen in prior art FIG. 2, the fuel pump 18 is axially driven by a drive shaft 26 associated with a motor 28 located on an opposite face 30 of the housing 12. The drive shaft 26 also drives a blower wheel 32 within the housing 12 for providing air into the air tube 14 for combustion via an air inlet portion 33 in the housing 12. The motor 28 is controlled by an electronic control module 34. The electronic control 34 operates to initiate delivery of oil, air and spark to the ignition head at 16 based on a call for heat from a thermostat (not shown), for example. The controller 34 may also operate to re-initiate ignition if combustion is discontinued unexpectedly and may further discontinue delivery of oil to the nozzle if ignition cannot be re-established within a predetermined lock-out time period (sometimes referred to as a safety lock-out condition).
Various types of controllers exist for oil burners. The controller 34 illustrated in prior art FIGS. 1 and 2 represents one basic type of controller that is used extensively. The controller 34 initiates air flow and fuel delivery substantially simultaneously via the motor drive shaft, while concurrently initiating spark at the head via a signal to the transformer 22. The above control methodology works well in many instances, however, since a fuel pressure at the nozzle during start-up may be less than the intended pressure, sufficient atomization of the fuel oil may not be established at start-up for robust combustion (i.e., a “rough” start). Accordingly, some control methodologies have adjusted the above procedure to improve combustion commencement by delaying the delivery of fuel to the nozzle until such time as the air flow has stabilized and the fuel pressure within the pump 18 has increased to near its steady state operating pressure. Such a delay is typically accomplished by a hydraulic valve circuit (not shown) within the fuel pump 18 or by a solenoid valve 19 having a valve activation which is delayed for a period of time after the air delivery and fuel pump are activated.
Since many of the basic style controllers highlighted above are in the field and operating adequately, replacement of the controller 34 with a more sophisticated controller having a timing delay therein incurs the cost of replacement of the controller, and thus in some cases is prohibitively expensive. Accordingly, use of a solenoid valve has been employed in various instances with a basic type controller. An external solenoid valve is typically mounted on the housing 12, typically near or on the pump 18 and is undesirably more complex and more costly than the standard arrangement. Furthermore, there may be interferences between the valve mounting and other necessary features of the burner, such as main power cordset routing. In addition, the valve undesirably takes space which is of concern because many burner units 10 are covered with an enclosure for safety and/or aesthetic reasons, and such additional space may impact the enclosure being employed.
One prior art solution to the above problem has been to integrate the solenoid valve into the pump and employ a negative temperature coefficient (NTC) current limiting device such as a thermistor within a connecting plug between the controller 34 and valve portion of the fuel pump 18 that allows an increasing amount of electric current to flow into the solenoid coil as the thermistor device heats up until the solenoid stem is actuated.
Although the prior art solutions have proven effective in many instances, it is always desirable to further improve delay systems for delivery of fuel oil to the nozzle for purposes of ignition.